70 BRITISH DESMIDIACEJ;. 



Length without spines 44-66 p, with spines 65-74 p, ; 

 breadth without spines 44-59 /x, with spines 62-72 ^ ; 

 breadth of isthmus 12-21 /n ; thickness 31 40 /A. 



ENGLAND. - -Westmoreland (Bissett). Strensall and 

 Pilmoor, N. Yorks ! Austwick Moss, W. Yorks I 

 Surrey! Cornwall! (Ralfs). 



WALES. --Capel Curig, Carnarvonshire! (Cooke $ 

 Wills). Dolgelly, Merionethshire (Rolfs). 



SCOTLAND. -- Sutherland !, Ross, Aberdeen, Kincar- 

 dine, Forfar, Perth, Argyll, Fife (Roy Bisxett). 

 Plankton of Loch Cuthaig, Lewis, Outer Hebrides I 

 Hoy, Orkneys ! 



IRELAND.- -Lough Anna, Donegal ! Berry dare 

 Lough, Ballynahinch, and lakes near Recess, Galway t 

 Dublin and Wicklow (Archer). 



Geogr. Distribution.- -France. Germany. Austria 

 (var.) and Galicia. Hungary. Italy. Norway. 

 [Sweden. Denmark. Finland. Poland. N. and S. 

 Russia. Greenland. X. India. W. and E. Africa 

 (var.). United States. Brazil. 



Xanthidium fasciculatum and X. antilopseum have in the 

 past been greatly confused, although the reasons for such 

 confusion are not altogether obvious. The spines of 

 X. antilopseum are somewhat variable, it is true, but no matter 

 what their number or disposition may be, -no form of this 

 species has the angularly reniform semicells of X. fascicu- 

 latum, neither does it possess six equidistant pairs of equal 

 spines. 



The central area is always slightly protuberant, and we 

 have invariably found it to possess granules, generally in the 

 form of a small ring surrounding two or three central ones. 

 It was upon this character that Nordstedt in 1885 based his 

 'var. ornatum/ Ralfs having 1 stated that his X.fasdeulatuiHVsar* 

 j3 polygonuin [which is X. fasciculatum Ehrenb. type] was 

 very near in the shape of its central projections to X. fascicu- 

 latum Ralfs var. a [which is X.antilopaeumffireb.} Kiitz.type] . 

 We consider both Ehrenberg's and llalfs' account of X. fas- 

 ciculatum to be confused and imperfect, and therefore to a 

 large extent unreliable. All the British, American, and 

 African specimens of X. fasciculatum we have examined have 

 possessed a granulated central area, and we conclude therefore 



